I’ll need this to be explained like I’m five because I’m no physicist. It seems from my reading that most scientists believe special relativity necessarily predicts that the past, present, and future already exist in a space time block universe. I don’t understand why the future has to necessarily exist. The way I try to think of space-time is that if I’m standing still, I move at “186,000 miles per hour” through the time dimension and as I move, my “speed” decreases and I begin moving through the space dimension. Physicists seem to be saying that the proof can be illustrated through the twin paradox - that the moving twin has moved into the future of the resting twin. But isn’t it the case that the twin slowed his movement through time and therefore isn’t in the future but just didn’t age as much yet? Where’s does the eternalist aspect come in?
I think it’s more fundamental and philosophical than that. You’re correct about how the speed of moving through the space and time dimensions are correlated, (as I understand,) but they’re also dimensions on the same map, as it were.
Consider, for instance, a map on which you’ve wandered from east to west all your life, but also always traveled south, never returned to the north. Would you say that the lands to the south of you “already exist”, even if you haven’t gotten there yet and never saw them? Even if nobody you’ve ever spoken to has seen the lands of the south?
I have to admit, I can’t see where the twin paradox is supposed to illuminate this.
I’m not sure how the twin paradox shows that the future already exist.
The twin paradox highlights the fact that time moves at different rates depending on how fast you travel.
The faster you travel, the slower time moves.
Take two identical atomic clocks, place one at an airport. Then place the other on an airplane. When the airplane returns, it’s clock will display a time slower than the stationary one. Perhaps as little as a .00001 second difference, but a difference nonetheless.
Ramp that up with close to lightspeed travel, throw in some twins instead of atomic clocks. When one twin returns from his space voyage, he will find his twin to be an old man.
Do you distinguish between future and past in this question? If you are bothered by the past but neglected to mention it, then skip the rest of this paragraph. OTOH, if you accept the idea that the past exists, and it is only the future that bothers you, then you need to ask yourself why you are prejudiced in this manner. Why is one more real than the other? The only difference I can see is that we have memories of one, but no memories of the other, and that seems awfully subjective, no?
Try this: According to relativity, there is no objective standard for “simultaneous”. If I ask whether A occurred before B or B occurred before A, then according to relativity, the answer must be, “Well, that depends on where you were located in relation to A and to B, and how fast you were going and in which direction.” - because depending on those factors, either of them might have been “first”. And if either might have been first, and we accept both of them as being real, then each one’s future is just as real as the other one’s past. Or something like that. This stuff is very confusing and gives me headaches.
The twin paradox doesn’t require that a future “already” exists, it just explains how they can be different ages when they get there.
Existence means “having objective reality.” Neither the past nor future are part of objective reality. Neither can be observed nor measured. They exist only as subjective ideas. The only thing that exists is the now.
In relativity there is no preferred frame of reference (e.g. one frame of reference is someone sitting on a train moving at some speed and another is a person standing at the train station watching it go by). Different frames will observe the same event differently. For instance of you are bouncing a ball on the train it seems to go straight up and down to you. The person on the train platform sees the ball going up and down and moving forward.
This can lead to weird results. It is possible for two observers to disagree on the order of events. E.g. what happened first and what happened second. Thing is BOTH are correct. Watch this video to get an idea of how that works.
So, this means you can see things that happens in someone else’s future. From their perspective it has not happened yet. From yours it has.
So, therefore, the future must already exist because someone else can perceive it.
Here is a quick video illustrating simultaneity. From this you can see the person on the platform can see something that happens in the person on the train’s future.
Yes I’ve seen a lot of those examples but they always seem to be the result of of the photons getting to one person faster rather than seeing the future.
I’d tackle this a bit differently. People keep talking about “the future” without examining the “the” part. “The future” is not a single unified synchronized thing. Neither was “the past”.
Any one of us (or indeed any sub-c particle) has the experience of a single unified future-becoming-present-becoming-past.
Any two of us do not.
Instead we each have individual streams of future-becoming-present-becoming-past that slide “ahead” and “behind” each other based on how our relative speeds change. Or, more precisely, how we are accelerated. Sort of like two horses racing neck-and-neck: one or the other may pull ahead or slide back relative to the other even as both are rushing headlong towards the next turn.
As a result, talking about “the future” is wrong. There is my future, your future, some futures, several futures, etc. There is never “the future”.
As a separate matter, I am not real comfortable that anyone has a clear idea of what “exist” even means in the context of time. Many of us use that word, but do we agree on what it means in the way we agree that, say, Madagascar “exists” even though none of us are there to experience it directly?
Well you’re speaking ontologically, but Einstein believed the future already exists - like a 4th or 5th dimensional being could see my eventual death now.
Yeah.
But remember from the perspective of the person on the train (in that video) the lightning strike is in her future. The person on the platform knows it has happened. So he has seen an event in her future.
Nothing can go faster than that photon.
Try this video. Watch for seven minutes and I think you will get it. Much better than the other ones. Mind exploding stuff.
Einstein also argued against Quantum Mechanics.
I’m not sure whether the practitioners of Special Relativity genuinely believe that the future is simply a few calculations away from being solvable. Since there’s no randomness in the formulae, that would be the implication if you had sufficient information.
But remember that Special Relativity and Quantum Mechanics haven’t yet been joined together. The information isn’t generated until a case pops up that requires it. Until that point, the state of all the inputs varies across a certain probability field.
I think what the OP is referring to is Minkowski spacetime, where space and time are unified into one four-dimensional structure. In this view, each event is a point in spacetime. It’s easiest to work with this model if you view the whole structure as existing as one entity, so that light cones are easily visualized, you can calculate the spacetime interval between events, and so on.
Whether this view implies that the future “exists” is really a philosophical question of how you want to interpret the mathematics. It’s not even clear what is meant by “the future already exists”, since the word “already” (or any equivalent formulation in everyday language) implies a commonsense view of time that is different from viewing time as one of the four spacetime dimensions. I don’t know if it’s accurate to say that most scientists believe the future already exists. I would say most scientists (who work in this area) view it as convenient to do their calculations as if the four dimensional spacetime block exists, because doing so gives the correct answers and simplifies calculations. What it implies about reality is a separate question. It could be that this spacetime view is far removed from reality, and just happens to give the correct answers, like Ptolemy’s epicycles gave (approximately) correct predictions about the movements of the planets even though his model is far removed from reality.
Actually, no: the Special Relativity equations govern “events” not perceptions of those events. When you factor in the time for photons to go from the event to the observer, the math gets even hairier. But that isn’t necessary for the basic concept.
The two events, themselves, can exist in either order – A then B, or B then A – or simultaneously – in and of themselves, without regard to observation lag.
(Or, if you prefer, the observation lag can be factored out.)
I happened to be downstairs, sharpening my tools, when the massive gamma ray burst killed everything in my garden. The floor of my house is very thick, so I survived to see another beautiful twin sunset from the back porch on Alpha Centauri Bb. So, I know where that burst came from, and it is headed your way. It will reach you in several of your years (less than 4, because it was not quite directly opposite me). I would so like to warn you, because, while it will probably not kill everything like it did here, it will surely mess you up. Sadly, there is no way for me to do this, because the burst will arrive before any message I could possibly send you.
So, your future is determined. I have witnessed it, in a way. What the exact effects will be are uncertain – perhaps your astronomers will have a system in place that will predict the burst event – but either way you slice it, there is not a lot you can to to make it less ugly. Good luck to you, hope things turn out better for you than they did for me (we have seeds and stores, so we will recover).
That’s not what is happening here.
Yours is a prediction. A good one but still a prediction.
The OP means the future and past actually exists the same as the present. As in you being able to see the earth getting hit by the gamma ray burst (not just predict it) before the people on earth experience the gamma ray burst.
I’ve watched that video many times before and I don’t get it at all. I’ve read a lot of stuff about SR and it all makes sense to me. I get that mass increases and length contracts along the line of motion. I understand the light experiments, but this video makes no sense to me. I don’t understand why the distance between them matters and what he means by the aliens now slice is in our future.
It isn’t about photons. Due to photons being massless they travel at c. That is just a convenient coincidence. What matters is that nothing travels faster than the speed of causality, (including travel in time.) No action at all that affects something else that is separated from the source of the action, in either time or space, can cause the effect in a shorter time than it takes to cover the distance (in either time or space) at the speed of causality.
From here it is possible to construct simple examples where the order of events as seen by different observers is different. It doesn’t matter how they observe events, or indeed in which dimension they are observing them.
The limited speed of causality means that your local reality is all you have. There are an infinitude of other possible ordering of external events and realities. This is why causality and locality are so important. (And why EPR and spooky action at a distance are so worrying.)
The most simple answer, the future always exists for the same reason that “up” always exists.
While there are some exceptions related to causality time is just one of the 4 dimensions that make up “spacetime”
In spacetime your “world line” (if we ignore the fact that what is “you” gradually changes over time) is you, for your entire existence.
Now there is a question about free will here that I cannot address without math but the fact that your worldline exists does not necessarily mean that things are pre-determaned in a way that you would think of as fate.
Really the main implication is that the only thing that you can make sure observers can agree on is the spacetime interval. These observers may or may not agree on the timing of events, simultaneous of events, order of events etc… but they will always agree on the space time interval. (if they can observe the event)
There is speculation and implications about free will in GR, but those tend to be either speculation on yet to be settled science or are conflating conflating the human construct of “spacetime” as an intuitive map of all time.
If anyone else can point me at an tested theories on a predetermined future I would appropriate it but I doubt if it will ever be testable due to Hawking’s speech I saw back in the 80s
“Not only does God play dice, but… he sometimes throws them where they cannot be seen.”
But really even if you could know the state of the entire universe at one time this may likely not hold up once they find a way to merge GR and QM.
That said, the world-line in spacetime is very useful but it does not to my knowledge strictly allow you to predict the future without knowing everything about the entire universe at one time. Which may be true but will never be possible (and only if you ignore the unsolved quantum issues)